JP2020167245A - Fiber laser device - Google Patents

Abstract

To provide a fiber laser device capable of reducing possibility of heat evolution and failure resulting from residual excitation light.SOLUTION: A fiber laser device 1 includes an optical fiber 10 for amplification, a front excitation light source 21 generating exciting light P1 of wavelength λ1, and capable of introducing the exciting light P1 from the upstream side of the optical fiber 10 for amplification to a cladding layer 12 of the optical fiber 10 for amplification, a rear excitation light source 22 generating exciting light P2 of wavelength λ2, and capable of introducing the exciting light P2 from the downstream side of the optical fiber 10 for amplification to the cladding layer 12 of the optical fiber 10 for amplification, an upstream side optical filter part 50 to be connected between the front excitation light source 21 and the optical fiber 10 for amplification, and a downstream side optical filter part 60 to be connected between the rear excitation light source 22 and the optical fiber 10 for amplification. The upstream side optical filter part 50 is configured to restrain permeation of the light of wavelength λ2, while allowing permeation of the light of wavelength λ1. The downstream side optical filter part 60 is configured to restrain permeation of the light of wavelength λ1, while allowing permeation of the light of wavelength λ2.SELECTED DRAWING: Figure 1

Description

The present invention relates to a fiber laser device, and more particularly to a bidirectional excitation type fiber laser device.

Conventionally, in a fiber laser apparatus, for example, a double clad fiber in which an inner clad and an outer clad are formed around a core may be used (see, for example, Patent Document 1). In this type of double clad fiber, excitation light is incident on the inner clad that covers the periphery of the core, and the excitation light propagates through this inner clad as a waveguide. In the optical amplification unit, when the excitation light propagating in the inner cladding passes through the core, the rare earth element ions added to the core are excited by the excitation light, and the signal light is amplified.

As a method for introducing such excitation light into the optical amplification unit, a bidirectional excitation type method in which excitation light is introduced from both sides of the optical amplification unit is known. This bidirectional excitation type system can introduce twice as much excitation light into the optical amplification unit as compared to the case where the excitation light is introduced from one side of the optical amplification unit, and is therefore used for further increasing the output of the fiber laser device. Is expected.

In the fiber laser device described above, of the excitation light propagating in the inner clad, the excitation light not absorbed by the core of the optical amplification unit becomes residual excitation light and propagates in the inner clad. In the case of a double-excitation type fiber laser apparatus, if the excitation light introduced from one excitation light source becomes the residual excitation light without being absorbed by the core of the optical amplification unit, the residual excitation light reaches the other excitation light source. It is considered that this may cause the reliability of the excitation light source to decrease. In particular, with the increase in output of laser devices in recent years, the power of such residual excitation light is also increasing, so that the problem of residual excitation light is becoming more prominent.

International Publication No. 2013/001734

The present invention has been made in view of such problems of the prior art, and an object of the present invention is to provide a fiber laser apparatus capable of reducing the possibility of heat generation and failure due to residual excitation light.

According to one aspect of the present invention, there is provided a fiber laser apparatus capable of reducing the possibility of heat generation and failure due to residual excitation light. This fiber laser device has an amplification optical fiber including a core to which rare earth element ions are added, a clad layer having an optical waveguide capable of propagating excitation light for exciting the rare earth element ions, and a first wavelength. At least one first excitation light source capable of generating the first excitation light and introducing the first excitation light into the clad layer of the amplification optical fiber from the first end side of the amplification optical fiber. Then, a second excitation light having a second wavelength different from the first wavelength is generated, and the first clad layer of the amplification optical fiber is formed from the second end side of the amplification optical fiber. It includes at least one second excitation light source into which the second excitation light can be introduced, and a first optical filter unit connected between the at least one first excitation light source and the amplification optical fiber. The first optical filter unit is configured to allow the transmission of light of the first wavelength and suppress the transmission of light of the second wavelength. The peak of the absorption spectrum for the rare earth element ion at the second wavelength may be lower than the peak of the absorption spectrum for the rare earth element ion at the first wavelength.

According to such a configuration, of the second excitation light introduced from the second excitation light source into the inner cladding of the amplification optical fiber, the residual excitation light that is not absorbed by the core of the amplification optical fiber is the first. Propagation beyond the optical filter section of the light source is suppressed. Therefore, it is possible to reduce the possibility of heat generation and failure of the first excitation light source due to the residual excitation light caused by the second excitation light.

The first optical filter unit may be configured to transmit the light of the first wavelength and reflect the light of the second wavelength. More specifically, the first optical filter unit includes a core and a plurality of clad layers arranged around the core, and the plurality of clad layers of the first optical filter unit are at least the above. It may include an excitation light propagation clad layer that forms a first excitation optical waveguide through which the first excitation light propagates. The excitation light propagation clad layer of the first optical filter section has a clad grating section whose refractive index periodically changes along the optical axis direction so as to reflect at least a part of the second excitation light. You may be doing it.

In this way, by configuring the first filter unit so that the light of the first wavelength is transmitted and the light of the second wavelength is reflected, the second of the second wavelength toward the first excitation light source is formed. The excitation light of the above can be reflected by the first optical filter unit and returned to the amplification optical fiber. By returning the second excitation light to the amplification optical fiber in this way, the second excitation light can be reabsorbed by the core of the amplification optical fiber, so that the output efficiency of the fiber laser apparatus is improved.

The core of the first optical filter unit has a core grating unit whose refractive index periodically changes along the optical axis direction so as to reflect light having a wavelength amplified by the amplification optical fiber. You may. By forming such a core grating section, the first optical filter section can be used as the fiber Bragg grating section constituting the optical resonator. In this case, the fiber Bragg grating portion of the optical resonator used in the conventional fiber laser apparatus can be integrated with the first filter portion. Therefore, the number of fusion splicing points is reduced to reduce the optical loss, and the number of parts is reduced to reduce the manufacturing cost.

The at least one first excitation light source includes a plurality of first excitation light sources, and the fiber laser apparatus combines the first excitation lights from the plurality of first excitation light sources to obtain the amplification light. It is preferable to further include a first optical combiner to be introduced into the fiber. By including a plurality of excitation light sources in this way, it is possible to increase the output of the fiber laser device.

In this case, the first optical filter unit may be provided between the first optical combiner and the amplification optical fiber. Such a first optical filter unit suppresses the propagation of the second excitation light that was not absorbed by the core of the amplification optical fiber beyond the first optical filter unit to the first optical combiner. .. Therefore, it is possible to reduce the possibility of heat generation and failure of the first optical combiner due to the residual excitation light caused by the second excitation light.

Alternatively, the first optical filter unit may be connected between at least one of the plurality of first excitation light sources and the first optical combiner. In this case, it is preferable that the first optical filter unit is configured to suppress the transmission of light having a wavelength of signal light. According to such a configuration, the signal light amplified by the amplification optical fiber together with the second excitation light that was not absorbed by the core of the amplification optical fiber passes through the first optical filter unit and is first excited. Propagation to the light source is suppressed. Therefore, it is possible to reduce the possibility of heat generation and failure of the first excitation light source due to the second excitation light and the signal light.

The fiber laser device may further include a second optical filter unit connected between the at least one second excitation light source and the amplification optical fiber. The second optical filter unit is configured to suppress the transmission of the light of the first wavelength while allowing the transmission of the light of the second wavelength. According to such a configuration, of the first excitation light introduced from the first excitation light source into the inner cladding of the amplification optical fiber, the residual excitation light that is not absorbed by the core of the amplification optical fiber is the second. Propagation beyond the optical filter section of the light source is suppressed. Therefore, it is possible to reduce the possibility of heat generation and failure of the second excitation light source due to the residual excitation light caused by the first excitation light.

The second optical filter unit may be configured to transmit the light of the second wavelength and reflect the light of the first wavelength. More specifically, the second optical filter unit includes a core and a plurality of clad layers arranged around the core, and the plurality of clad layers of the second optical filter unit are at least the above. It may include an excitation light propagation clad layer that forms a second excitation optical waveguide through which the second excitation light propagates. The excitation light propagation clad layer of the second optical filter unit has a clad grating portion whose refractive index periodically changes along the optical axis direction so as to reflect at least a part of the first excitation light. You may be doing it.

In this way, by configuring the second filter unit so that the light of the second wavelength is transmitted and the light of the first wavelength is reflected, the first of the first wavelength toward the second excitation light source is formed. The excitation light of the above can be reflected by the second optical filter unit and returned to the amplification optical fiber. By returning the first excitation light to the amplification optical fiber in this way, the first excitation light can be reabsorbed by the core of the amplification optical fiber, so that the output efficiency of the fiber laser apparatus is improved.

The core of the second optical filter unit has a core grating unit whose refractive index periodically changes along the optical axis direction so as to reflect light having a wavelength amplified by the amplification optical fiber. You may. By forming such a core grating section, a second optical filter section can be used as the fiber Bragg grating section constituting the optical resonator. In this case, the fiber Bragg grating portion of the optical resonator used in the conventional fiber laser apparatus can be integrated with the second filter portion. Therefore, the number of fusion splicing points is reduced to reduce the optical loss, and the number of parts is reduced to reduce the manufacturing cost.

The at least one second excitation light source includes a plurality of second excitation light sources, and the fiber laser apparatus combines the second excitation lights from the plurality of second excitation light sources to form the amplification light. It is preferable to further include a second optical combiner to be introduced into the fiber. By including a plurality of excitation light sources in this way, it is possible to increase the output of the fiber laser device.

The second optical filter unit may be provided between the second optical combiner and the amplification optical fiber. Such a second optical filter unit suppresses the propagation of the first excitation light that was not absorbed by the core of the amplification optical fiber to the second optical combiner beyond the second optical filter unit. .. Therefore, it is possible to reduce the possibility of heat generation and failure of the second optical combiner due to the residual excitation light caused by the first excitation light.

Alternatively, the second optical filter unit may be connected between at least one of the plurality of second excitation light sources and the second optical combiner. In this case, it is preferable that the second optical filter unit is configured to suppress the transmission of light having a wavelength of signal light. According to such a configuration, the signal light amplified by the amplification optical fiber together with the first excitation light that is not absorbed by the core of the amplification optical fiber passes through the second optical filter unit and is excited by the second excitation. Propagation to the light source is suppressed. Therefore, it is possible to reduce the possibility of heat generation and failure of the second excitation light source due to the first excitation light and the signal light.

According to the present invention, it is possible to reduce the possibility of heat generation and failure due to the residual excitation light.

FIG. 1 is a schematic block diagram showing the overall configuration of the fiber laser apparatus according to the first embodiment of the present invention. FIG. 2 is a cross-sectional view schematically showing the structure of an optical fiber for amplification in the fiber laser apparatus of FIG. FIG. 3 is a cross-sectional view schematically showing an example of a configuration when the upstream optical filter portion of the fiber laser apparatus of FIG. 1 is cut along a plane perpendicular to the optical axis. FIG. 4 is a cross-sectional view schematically showing an example of a configuration when the upstream side optical filter portion of FIG. 3 is cut along a plane parallel to the optical axis. FIG. 5 is a cross-sectional view schematically showing a configuration when the downstream optical filter portion of the fiber laser apparatus of FIG. 1 is cut along a plane parallel to the optical axis. FIG. 6A is a diagram for explaining an example of a method of manufacturing the downstream side optical filter portion of FIG. 5 or the upstream side optical filter portion of FIG. FIG. 6B is a diagram for explaining another example of a method of manufacturing the downstream side optical filter portion of FIG. 5 or the upstream side optical filter portion of FIG. FIG. 7 is a schematic block diagram showing the overall configuration of the fiber laser apparatus according to the second embodiment of the present invention. FIG. 8 is a cross-sectional view schematically showing an example of a configuration when the upstream optical filter portion of the fiber laser apparatus of FIG. 7 is cut along a plane parallel to the optical axis. FIG. 9 is a cross-sectional view schematically showing an example of a configuration when the downstream optical filter portion of the fiber laser apparatus of FIG. 7 is cut along a plane parallel to the optical axis. FIG. 10A is a diagram for explaining an example of a method of manufacturing the downstream side optical filter portion of FIG. 9 or the upstream side optical filter portion of FIG. FIG. 10B is a diagram for explaining another example of a method of manufacturing the downstream side optical filter portion of FIG. 9 or the upstream side optical filter portion of FIG. FIG. 11 is a schematic block diagram showing the overall configuration of the fiber laser apparatus according to the third embodiment of the present invention. FIG. 12 is a schematic block diagram showing the overall configuration of the fiber laser apparatus according to the fourth embodiment of the present invention.

Hereinafter, embodiments of the fiber laser apparatus according to the present invention will be described in detail with reference to FIGS. 1 to 12. In FIGS. 1 to 12, the same or corresponding components are designated by the same reference numerals, and duplicate description will be omitted. Further, in FIGS. 1 to 12, the scale and dimensions of each component may be exaggerated or some components may be omitted.

FIG. 1 is a schematic block diagram showing the overall configuration of the fiber laser apparatus 1 according to the first embodiment of the present invention. As shown in FIG. 1, the fiber laser apparatus 1 in the present embodiment can introduce the excitation light P ₁ into the optical resonator 2 including the optical fiber 10 for amplification and the optical resonator 2 from the upstream side of the optical resonator 2. Upstream optical combiner 31 (first light) capable of combining a plurality of forward excitation light sources 21 (first excitation light source) and excitation light P ₁ from these forward excitation light sources 21 and outputting them to the optical cavity 2. Combiner), a plurality of rear excitation light sources 22 (second excitation light sources) capable of introducing excitation light P ₂ into the optical resonator 2 from the downstream side of the optical resonator 2, and excitation light from these rear excitation light sources 22. At the downstream end of the delivery fiber 40, the downstream optical combiner 32 (second optical combiner) that can combine P ₂ and output to the optical resonator 2, the delivery fiber 40 extending from the downstream optical combiner 32, and the delivery fiber 40. The provided laser emitting section 41, the upstream optical filter section 50 (first optical filter section) connected between the amplification optical fiber 10 and the upstream side optical combiner 31, and the amplification optical fiber 10 and downstream. It is provided with a downstream side optical filter unit 60 (second optical filter unit) connected to the side optical combiner 32. In the present specification, unless otherwise specified, the direction in which the laser beam L is emitted from the optical resonator 2 is referred to as "downstream side", and the direction opposite to that is referred to as "upstream side". To do.

FIG. 2 is a cross-sectional view schematically showing the structure of the amplification optical fiber 10. As shown in FIG. 2, the amplification optical fiber 10 includes a core 11 to which rare earth element ions such as ytterbium (Yb), erbium (Er), and yttrium (Y) are added, and an inner clad layer that covers the periphery of the core 11. It has 12 and an outer clad layer 13 that covers the periphery of the inner clad layer 12. The refractive index of the inner clad layer 12 is lower than that of the core 11, and an optical waveguide is formed inside the core 11. The refractive index of the outer clad layer 13 is lower than the refractive index of the inner clad layer 12, and an optical waveguide is also formed inside the inner clad layer 12.

As shown in FIG. 1, the optical resonator 2 is formed in a high reflection fiber Bragg grating section (high reflection FBG section) 14 formed in the upstream portion of the amplification optical fiber 10 and a downstream portion of the amplification optical fiber 10. The low-reflection fiber Bragg grating section (low-reflection FBG section) 16 is included. The high-reflection FBG unit 14 is formed by periodically changing the refractive index of the core along the optical axis direction, and reflects light in a predetermined wavelength band with a reflectance close to 100%. Like the high-reflection FBG section 14, the low-reflection FBG section 16 is formed by periodically changing the refractive index of the core along the optical axis direction, and is a wavelength band reflected by the high-reflection FBG section 14. It allows a part (for example, 90%) of the light to pass through and reflects the rest.

For example, when Yb is added to the core 11 of the amplification optical fiber 10, the forward excitation light source 21 is composed of a high-power multimode semiconductor laser having an oscillation wavelength of 975 nm, and is an excitation light having a wavelength of 975 nm (= λ ₁ ). It produces P ₁ . The rear excitation light source 22 is composed of, for example, a high-power multimode semiconductor laser having an oscillation wavelength of 915 nm, and generates excitation light P ₂ having a wavelength of 915 nm (= λ ₂ ). In this example, the absorption spectra for Yb ions is higher than the peak towards the peak at a wavelength lambda ₁ is the wavelength lambda _2, than the excitation light P ₂ having a wavelength lambda ₂ is towards the pump light P ₁ of the wavelength lambda ₁ amplification It is easily absorbed by the core 11 of the optical fiber 10.

The upstream optical combiner 31 is configured to combine the excitation light P ₁ of wavelength λ ₁ output from the forward excitation light source 21 and introduce the excitation light P ₁ into the inner clad layer 12 of the amplification optical fiber 10. ing. Further, the downstream optical combiner 32 combines the excitation light P ₂ of the wavelength λ ₂ output from the rear excitation light source 22 and introduces the excitation light P ₂ into the inner clad layer 12 of the amplification optical fiber 10. It is configured. Thus, the optical waveguide is formed on the inside of the inner cladding layer 12 of the amplification optical fiber 10, the pumping light P ₁ having a wavelength lambda ₁ from the upstream side is introduced from the downstream side of the wavelength lambda ₂ pumping light P ₂ Is introduced.

In the optical resonator 2, the excitation light P ₁ and the excitation light P ₂ propagating in the inner clad layer 12 of the amplification optical fiber 10 are each absorbed by the rare earth element ions when passing through the core 11, and the rare earth element ions are absorbed. Excited to produce naturally emitted light. This naturally emitted light is recursively reflected between the high-reflection FBG section 14 and the low-reflection FBG section 16, and light having a specific wavelength λ ₃ (for example, 1064 nm) is amplified to cause laser oscillation. The laser light (hereinafter referred to as “signal light”) L of wavelength λ ₃ amplified by the optical resonator 2 propagates in the core 11 of the amplification optical fiber 10, and a part of the laser light passes through the low reflection FBG unit 16. And propagate to the downstream side. The laser beam L transmitted through the low-reflection FBG unit 16 is emitted from the laser emitting unit 41 through the delivery fiber 40 toward, for example, the workpiece.

The upstream side optical filter unit 50 allows the transmission of the excitation light P ₁ of the wavelength λ ₁ output from the front excitation light source 21, but allows the transmission of the excitation light P ₂ of the wavelength λ ₂ output from the rear excitation light source 22. It is configured to suppress. For example, certain absorbent (e.g. saturable absorber (SESAM (semiconductor saturable absorber mirror), such as carbon nanotubes and graphene)) using a wavelength lambda ₂ of the pumping light P ₂ absorbs Although excitation wavelengths lambda ₁ The upstream optical filter unit 50 can be configured so as not to absorb the light P ₁ . In this case, the outputs of the front excitation light source 21 and the rear excitation light source 22 may be controlled so that the absorption of the excitation light P ₁ is larger than the absorption of the excitation light P ₂ . Further, even if such control is not performed, since the upstream side light filter unit 50 is directly connected to the front excitation light source 21, the light intensity of the excitation light P ₁ from the front excitation light source 21 is high and the upstream side light filter Although it is transmitted without being absorbed by the unit 50, since there is an optical resonator 2 between the upstream light filter unit 50 and the rear excitation light source 22, the excitation light from the rear excitation light source 22 to the upstream light filter unit 50 is transmitted. It is conceivable that P ₂ is a residual component and has a low light intensity, and the excitation light P ₂ having a light intensity equal to or lower than the light intensity that can be absorbed by the absorbent material is absorbed by the upstream light filter unit 50.

Further, it is possible to configure the upstream optical filter unit 50 so as to separate the light (excitation light P ₂ having a wavelength lambda ₂₎ of a particular wavelength to the outside by using an optical coupler. Alternatively, a fiber Bragg grating technology, as described later, it is the pumping light P ₂ having a wavelength lambda ₂ is reflected constituting the upstream-side filter part 50 as excitation light P ₁ of the wavelength lambda ₁ is transmitted it can.

The downstream side optical filter unit 60 allows the transmission of the excitation light P ₂ of the wavelength λ ₂ output from the rear excitation light source 22, but the transmission of the excitation light P ₁ of the wavelength λ ₁ output from the front excitation light source 21. It is configured to suppress. For example, certain absorbent (e.g. saturable absorber (SESAM (semiconductor saturable absorber mirror), such as carbon nanotubes and graphene)) using a wavelength lambda ₁ of the pump light P ₁ absorbs Although excitation wavelength lambda ₂ The downstream optical filter unit 60 can be configured so as not to absorb the light P ₂ . In this case, the outputs of the front excitation light source 21 and the rear excitation light source 22 may be controlled so that the absorption of the excitation light P ₂ is larger than the absorption of the excitation light P ₁ . Further, even if such control is not performed, since the downstream side optical filter unit 60 is directly connected to the rear excitation light source 22, the light intensity of the excitation light P ₂ from the rear excitation light source 22 is high and the downstream side optical filter Although it is transmitted without being absorbed by the unit 60, since there is an optical resonator 2 between the downstream side optical filter unit 60 and the front excitation light source 21, the excitation light from the front excitation light source 21 to the downstream side optical filter unit 60 It is conceivable that P ₁ is a residual component and has a low light intensity, and the excitation light P ₁ having a light intensity equal to or lower than the light intensity that can be absorbed by the absorbent material is absorbed by the downstream optical filter unit 60.

Further, it is possible to configure the downstream optical filter unit 60 so as to isolate a particular wavelength light (wavelength lambda ₁ of the pumping light P ₁₎ to the outside by using a light coupler. Alternatively, a fiber Bragg grating technology as described below, be the pump light P ₁ of the wavelength lambda ₁ is the excitation light P ₂ of but reflects the wavelength lambda ₂ constitutes the downstream-side optical filter 60 so as to transmit it can.

In the fiber laser apparatus 1 having such a configuration, the excitation light P ₁ having a wavelength λ ₁ emitted from each of the forward excitation light sources 21 is coupled by the upstream optical combiner 31 and is located on the downstream side of the upstream optical combiner 31. It reaches the upstream side optical filter unit 50. Since the upstream optical filter unit 50 allows the excitation light P _{1 having} a wavelength of λ ₁ to pass through, the excitation light P ₁ is introduced into the inner clad layer 12 of the amplification optical fiber 10. The excitation light P ₁ introduced into the amplification optical fiber 10 is absorbed by rare earth element ions when passing through the core 11, but the excitation light (residual excitation light) P ₁ not absorbed by the core 11 is for amplification. It reaches the downstream side optical filter unit 60 located on the downstream side of the optical fiber 10. Since the downstream side optical filter unit 60 is configured to suppress the transmission of the excitation light P _{1 having} the wavelength λ ₁ , the downstream side optical filter unit 60 moves the downstream side optical filter unit 60 to the downstream side of the downstream side optical filter unit 60. The propagation of the residual excitation light P ₁ is suppressed. Therefore, the residual excitation light P ₁ is suppressed from reaching the downstream side optical combiner 32 and the rear excitation light source 22, and the possibility of heat generation and failure of the downstream side optical combiner 32 and the rear excitation light source 22 due to the residual excitation light P ₁ is reduced. Will be done.

Further, the excitation light P ₂ having a wavelength λ ₂ emitted from each of the rear excitation light sources 22 is coupled by the downstream side optical combiner 32 and reaches the downstream side optical filter unit 60 located on the upstream side of the downstream side optical combiner 32. .. Since the downstream optical filter unit 60 allows the excitation light P _{2 having} a wavelength of λ ₂ to be transmitted, the excitation light P ₂ is introduced into the inner clad layer 12 of the amplification optical fiber 10. The excitation light P ₂ introduced into the amplification optical fiber 10 is absorbed by rare earth element ions when passing through the core 11, but the excitation light (residual excitation light) P ₂ not absorbed by the core 11 is for amplification. It reaches the upstream side optical filter unit 50 located on the upstream side of the optical fiber 10. Since the upstream side optical filter unit 50 is configured to suppress the transmission of the excitation light P _{2 having} a wavelength of λ ₂ , the upstream side optical filter unit 50 moves the upstream side optical filter unit 50 to the upstream side of the upstream side optical filter unit 50. The propagation of the residual excitation light P ₂ is suppressed. Therefore, the residual excitation light P ₂ is suppressed from reaching the upstream side optical combiner 31 and the front excitation light source 21, and the possibility of heat generation and failure of the upstream side optical combiner 31 and the front excitation light source 21 due to the residual excitation light P ₂ is reduced. Will be done.

Here, in order to suppress the transmission of the upstream side of the pumping light P ₂ upstream optical filter unit 50, the upstream-side filter part 50 reflects the excitation light P ₂ having a wavelength lambda _2, the wavelength lambda ₁ of It is preferable that it is configured to transmit the excitation light P ₁ . When the excitation light P ₂ is reflected by the upstream optical filter unit 50 in this way, the residual excitation light P ₂ toward the upstream side is reflected by the upstream optical filter unit 50 and returned to the amplification optical fiber 10. be able to. By returning this way the residual pump light P ₂ to the amplification optical fiber 10, the fiber output efficiency of the laser device 1 since it is possible to re-absorb the residual pump light P ₂ in the core 11 of the amplification optical fiber 10 Will increase. Further, it is also conceivable to return the residual pump light P ₂ is further backward pumping light source 22, the intensity of the residual pump light P ₂ is re-absorbed in the amplification optical fiber 10 becomes weaker, the residual pump light P ₂ Even if the rear excitation light source 22 is reached, the possibility of heat generation and failure of the rear excitation light source 22 is reduced. Hereinafter, an example of such an upstream optical filter unit 50 will be described.

FIG. 3 is a cross-sectional view schematically showing an example of a configuration when such an upstream optical filter unit 50 is cut on a plane perpendicular to the optical axis, and FIG. 4 is a cross-sectional view when the upstream optical filter portion 50 is cut on a plane parallel to the optical axis. It is sectional drawing which shows typically the structure of. As shown in FIGS. 3 and 4, the upstream optical filter unit 50 includes, for example, a core 51 made of SiO ₂ , an inner clad layer 52 that covers the periphery of the core 51, and an outer clad layer that covers the periphery of the inner clad layer 52. It has 53 and. Germanium (Ge), which is a dopant that imparts photosensitivity, is added to the inner clad layer 52. Since the addition of Ge increases the refractive index of the inner clad layer 52, boron (B) or fluorine (F), which is a dopant that lowers the refractive index, or a mixture of boron and fluorine is also added to the inner clad layer 52. ing. Since it has been reported that the photosensitivity is enhanced by adding Ge and B at the same time, it is preferable that both Ge and B are added to the inner clad layer 52 from the viewpoint of improving the photosensitivity. The core 51 and the inner clad layer 52 of the upstream optical filter unit 50 are optically coupled to the core 11 and the inner clad layer 12 of the amplification optical fiber 10, respectively.

The refractive index of the inner clad layer 52 is lower than that of the core 51. Further, the refractive index of the outer clad layer 53 is lower than the refractive index of the inner clad layer 52, and the excitation light P ₁ from the front excitation light source 21 can propagate inside the inner clad layer 52. An excited optical waveguide is formed. As described above, the inner clad layer 52 in the present embodiment is an excitation optical waveguide clad layer having a first excitation optical waveguide capable of propagating the excitation light P ₁ from the forward excitation light source 21.

As shown in FIG. 4, the inner clad layer 52 of the upstream side optical filter unit 50 has a clad grating portion 54 whose refractive index changes periodically along the optical axis direction. The clad grating portion 54 includes a plurality of refractive index changing portions 58 having a higher refractive index than the other portions 56 of the inner clad layer 52, and includes the other portions 56. These refractive index changing portions 58 are arranged at a predetermined lattice spacing d ₂ along the optical axis direction, and the refractive index thereof is lower than the refractive index of the core 51. The clad grating section 54 including such a refractive index changing section 58 reflects light having a wavelength λ _B represented by the following Bragg reflection equation (1).
λ _B = 2 × n _eff52 × d ₂・ ・ ・ (1)
Here, n _eff 52 is the effective refractive index of the propagation mode of the inner clad layer 52 of the upstream optical filter unit 50.

Since the wavelength of the excitation light P ₂ from the rear excitation light source 22 is λ ₂ , if the refractive index change portion 58 is formed at the lattice spacing d _{2 represented} by the following equation (2), the upstream side optical filter portion 50 The excitation light P ₂ having a wavelength λ ₂ propagating in the inner clad layer 52 is reflected by the clad grating portion 54 and returns to the downstream side as the reflected excitation light P ₂ '.
d ₂ = λ ₂ / (2 × n _eff52 ) ・ ・ ・ (2)

As described above, the excitation light P ₂ output from the rear excitation light source 22 is introduced into the amplification optical fiber 10, and the excitation light P ₂ introduced into the amplification optical fiber 10 is a rare earth element when passing through the core 11. The excitation light (residual excitation light) P ₂ absorbed by the ions but not absorbed by the core 11 propagates through the inner clad layer 52 of the upstream side optical filter unit 50 located on the upstream side of the amplification optical fiber 10. .. Since the residual excitation light P ₂ has a wavelength λ ₂ , it is reflected by the clad grating portion 54 of the upstream side optical filter unit 50 described above, and returns to the downstream side as the reflected excitation light P ₂ '. On the other hand, since the wavelength of the excitation light P ₁ output from the forward excitation light source 21 is λ ₁ and is different from the wavelength λ ₂ , the excitation light P ₁ from the front excitation light source 21 is clad grating of the upstream optical filter unit 50. It is transmitted as it is without being reflected by the part 54.

In this way, the upstream side optical filter unit 50 suppresses the propagation of the residual excitation light P ₂ to the upstream side of the upstream side optical filter unit 50, so that the residual excitation light P ₂ remains in the upstream side optical combiner 31 of FIG. It is possible to prevent the upstream optical combiner 31 from generating heat or being damaged due to the incident of the excitation light P ₂ . Further, it is possible to return to the amplification optical fiber 10 reflected excitation light P ₂ 'by reflecting residual pump light P ₂ by cladding grating portion 54 of the upstream-side filter part 50. 'By returning to the amplification optical fiber 10, the reflected excitation light P _2' thus reflected excitation light P ₂ of the fiber laser unit 1 so it is possible to re-absorb the core 11 of the amplification optical fiber 10 Output efficiency is increased. Further, 'it is conceivable to return more backward pumping light source 22, reflected excitation light P ₂ is re-absorbed in the amplification optical fiber 10' reflected excitation light P ₂ the strength of becomes weaker, the reflected excitation light P even ₂ 'has reached the backward pumping light source 22, the possibility of heat generation and failure of the backward pumping light source 22 is reduced.

The inside of the upstream optical filter unit 50 so that the residual excitation light P ₂ propagating in the inner clad layer 12 of the amplification optical fiber 10 is efficiently introduced into the inner clad layer 52 of the upstream optical filter unit 50. The outer diameter of the clad layer 52 is preferably equal to or larger than the outer diameter of the inner clad layer 12 of the amplification optical fiber 10. Also, as reflected excitation light P ₂ 'reflected by the clad grating portion 54 of the upstream-side filter part 50 is introduced effectively into the inner cladding layer 12 of the amplification optical fiber 10, the upstream-side filter part 50 It is more preferable that the outer diameter of the inner clad layer 52 is equal to the outer diameter of the inner clad layer 12 of the amplification optical fiber 10.

Similarly, in order to suppress the transmission of the downstream side of the pump light P ₁ downstream optical filter unit 60, the downstream-side filter part 60 reflects the excitation light P ₁ of the wavelength lambda _1, wavelength lambda ₂ It is preferable that it is configured to transmit the excitation light P ₂ . If the downstream side optical filter unit 60 is configured to reflect the excitation light P ₁ in this way, the downstream side optical filter unit 60 reflects the residual excitation light P ₁ toward the downstream side and returns it to the amplification optical fiber 10. be able to. By returning this way the residual pump light P ₁ to the amplification optical fiber 10, the fiber output efficiency of the laser device 1 since it is possible to re-absorb the residual pump light P ₁ in the core 11 of the amplification optical fiber 10 Will increase. Further, it is conceivable that the residual excitation light P ₁ further returns to the forward excitation light source 21, but since it is reabsorbed by the amplification optical fiber 10 and the intensity of the residual excitation light P ₁ is further weakened, the residual excitation light P ₁ is generated. Even if the forward excitation light source 21 is reached, the possibility of heat generation and failure of the front excitation light source 21 is reduced. Hereinafter, an example of such a downstream side optical filter unit 60 will be described.

FIG. 5 is a cross-sectional view schematically showing an example of a configuration when such a downstream side optical filter unit 60 is cut along a plane parallel to the optical axis. As shown in FIG. 5, the downstream side optical filter unit 60 has, like the upstream side optical filter unit 50, a core 61 made of, for example, SiO ₂ , an inner clad layer 62 that covers the periphery of the core 61, and an inner clad layer 62. It has an outer clad layer 63 that covers the periphery of the light. Germanium (Ge), which is a dopant that imparts photosensitivity, is added to the inner clad layer 62. Since the addition of Ge increases the refractive index of the inner clad layer 52, boron (B) or fluorine (F), which is a dopant that lowers the refractive index, or a mixture of boron and fluorine is also added to the inner clad layer 62. ing. Since it has been reported that the photosensitivity is enhanced by adding Ge and B at the same time, it is preferable that both Ge and B are added to the inner clad layer 62 from the viewpoint of improving the photosensitivity. The core 61 and the inner clad layer 62 of the downstream optical filter unit 60 are optically coupled to the core 11 and the inner clad layer 12 of the amplification optical fiber 10, respectively.

The refractive index of the inner clad layer 62 is lower than that of the core 61, and an optical waveguide capable of propagating the signal light L is formed inside the core 61. Further, the refractive index of the outer clad layer 63 is lower than the refractive index of the inner clad layer 62, and the excitation light P ₂ from the rear excitation light source 22 can propagate inside the inner clad layer 62. An excited optical waveguide is formed. As described above, the inner clad layer 62 in the present embodiment is an excitation optical waveguide clad layer having a second excitation optical waveguide capable of propagating the excitation light P ₂ from the rear excitation light source 22.

As shown in FIG. 5, the inner clad layer 62 of the downstream side optical filter unit 60 has a clad grating portion 64 whose refractive index changes periodically along the optical axis direction. The clad grating portion 64 includes a plurality of refractive index changing portions 68 having a higher refractive index than the other portions 66 of the inner clad layer 62, and includes the other portions 66. These refractive index changing portions 68 are arranged along the optical axis direction at a grid spacing d ₁ represented by the following equation (3), and the refractive index is lower than the refractive index of the core 61. ..
d ₁ = λ ₁ / (2 × n _eff62 ) ・ ・ ・ (3)
Here, n _eff 62 is the effective refractive index of the propagation mode of the inner clad layer 62 of the downstream optical filter unit 60. The clad grating section 64 including the refractive index changing section 68 arranged at such a lattice spacing d ₁ reflects the excitation light P ₁ having a wavelength λ ₁ propagating in the inner clad layer 62 of the downstream optical filter section 60.

The excitation light P ₁ output from the forward excitation light source 21 passes through the upstream side optical filter unit 50 as described above and is introduced into the amplification optical fiber 10. The excitation light P ₁ introduced into the amplification optical fiber 10 is absorbed by rare earth element ions when passing through the core 11, but the excitation light (residual excitation light) P ₁ not absorbed by the core 11 is for amplification. It propagates through the inner clad layer 62 of the downstream side optical filter unit 60 located on the downstream side of the optical fiber 10. Since the residual excitation light P ₁ has a wavelength λ ₁ , it is reflected by the clad grating portion 64 of the downstream side optical filter unit 60 described above, and returns to the upstream side as the reflected excitation light P ₁ '. On the other hand, since the wavelength of the excitation light P ₂ from the rear excitation light source 22 is λ ₂ and is different from the above wavelength λ ₁ , the excitation light P ₂ from the rear excitation light source 22 is the clad grating portion 64 of the downstream side optical filter unit 60. It is transmitted as it is without being reflected.

In this way, the downstream side optical filter unit 60 suppresses the propagation of the residual excitation light P ₁ to the downstream side of the downstream side optical filter unit 60, so that it remains in the downstream side optical combiner 32 of FIG. 1, for example. It is possible to prevent the downstream optical combiner 32 from being generated or damaged due to the incident of the excitation light P ₁ . Further, it is possible to return to the amplification optical fiber 10 reflected pump light P ₁ 'residual pump light P ₁ is reflected by the cladding grating portion 64 of the downstream-side filter part 60. 'By returning to the amplification optical fiber 10, the reflected excitation light P _1' thus reflected excitation light P ₁ of the fiber laser unit 1 so it is possible to re-absorb the core 11 of the amplification optical fiber 10 Output efficiency is increased. Further, 'it is conceivable to return to more forward pumping light source 21, reflected excitation light P ₁ is reabsorbed by the amplification optical fiber 10' reflected excitation light P ₁ because the strength of becomes weaker, the reflected excitation light P even ₁ 'reaches the forward pumping light source 21, the possibility of heat generation and failure of the forward pumping light source 21 is reduced.

The inside of the downstream side optical filter unit 60 so that the residual excitation light P ₁ propagating through the inner clad layer 12 of the amplification optical fiber 10 is efficiently introduced into the inner clad layer 62 of the downstream side optical filter unit 60. The outer diameter of the clad layer 62 is preferably equal to or larger than the outer diameter of the inner clad layer 12 of the amplification optical fiber 10. Also, as reflected excitation light P ₁ reflected by the clad grating portion 64 of the downstream-side optical filter 60 'is effectively introduced into the inner cladding layer 12 of the amplification optical fiber 10, the downstream-side filter part 60 It is more preferable that the outer diameter of the inner clad layer 62 is equal to the outer diameter of the inner clad layer 12 of the amplification optical fiber 10.

The upstream side optical filter unit 50 having the clad grating unit 54 and the downstream side optical filter unit 60 having the clad grating unit 64 can be manufactured by the following methods. For example, as shown in FIG. 6A, a base optical fiber (double) including a core 71 made of SiO ₂ , an inner clad layer 72 covering the periphery of the core 71, and an outer clad layer 73 covering the periphery of the inner clad layer 72. Clad fiber) 70 is prepared. No dopant is added to the core 71 of the base optical fiber 70.

On the other hand, germanium (Ge), which is a dopant that imparts photosensitivity, is added to the inner clad layer 72 of the base optical fiber 70. Since the addition of Ge increases the refractive index of the inner clad layer 72, boron (B), which is a dopant that lowers the refractive index, is also added to the inner clad layer 72. Fluorine (F) or a mixture of boron and fluorine may be added to the inner clad layer 72 instead of boron. Since it has been reported that the photosensitivity is enhanced by adding Ge and B at the same time, it is preferable to add both Ge and B to the inner clad layer 72 from the viewpoint of improving the photosensitivity. The amount of these Ge and B added is adjusted so that the refractive index of the inner clad layer 72 is lower than the refractive index of the core 71.

The base optical fiber 70 is irradiated with light (ultraviolet light) having a periodic intensity distribution along the optical axis direction from the radial direction by using a known method such as a phase mask method or a two-luminous flux interferometry. .. As a result, the refractive index of the inner clad layer 72 changes locally according to the intensity of the irradiated light, and this changed state lasts semipermanently. As a result, an optical filter unit having a clad grating unit whose refractive index changes periodically along the optical axis direction can be obtained. Such an optical filter unit can be used as the upstream side optical filter unit 50 or the downstream side optical filter unit 60 described above.

Since the dopant that gives photosensitivity is not added to the core 71 of the base optical fiber 70, the refractive index of the core 71 is not affected even if the core 71 is irradiated with the above ultraviolet rays.

As another example, as shown in FIG. 6B, at least one of aluminum (Al), phosphorus (P), and chlorine (Cl), which are dopants for increasing the refractive index, was added to SiO ₂ . A base material optical fiber (double clad fiber) 80 including a core 81, an inner clad layer 82 that covers the periphery of the core 81, and an outer clad layer 83 that covers the periphery of the inner clad layer 82 may be used. It is preferable that the dopant added to the core 81 does not have a function of increasing the photosensitivity. Only Ge, which is a dopant that imparts photosensitivity, is added to the inner clad layer 82, or B (or F or a mixture of B and F), which is a dopant that lowers the refractive index, is added in addition to Ge. By irradiating such a base material optical fiber 80 with ultraviolet light, it is possible to obtain an optical filter portion having a clad grating portion whose refractive index changes periodically along the optical axis direction. Such an optical filter unit can be used as the upstream side optical filter unit 50 or the downstream side optical filter unit 60 described above.

FIG. 7 is a schematic block diagram showing the overall configuration of the fiber laser apparatus 101 according to the second embodiment of the present invention. In the present embodiment, the upstream side optical filter unit 150 is provided in place of the upstream side optical filter unit 50 and the high reflection FBG unit 14 in the first embodiment, and the downstream side optical filter unit 60 in the first embodiment is provided. A downstream optical filter unit 160 is provided in place of the low reflection FBG unit 16.

FIG. 8 is a cross-sectional view schematically showing a configuration when the upstream side optical filter unit 150 is cut along a plane parallel to the optical axis. As shown in FIG. 8, the upstream side optical filter unit 150 of the present embodiment is a modified example of the upstream side optical filter unit 50 of the first embodiment shown in FIG. Like the upstream optical filter unit 50, the inner clad layer 52 of the upstream side optical filter unit 150 has a clad grating unit 154 whose refractive index changes periodically along the optical axis direction. The clad grating portion 154 includes the refractive index changing portions 158X and 158Y having a high refractive index.

Further, in the upstream side optical filter unit 150 of the present embodiment, the core 51 also has a core grating unit 155 whose refractive index changes periodically along the optical axis direction. The core grating section 155 includes refractive index changing sections 157X and 157Y having a high refractive index. The refractive index changing portions 158X and 158Y of the clad grating portion 154 and the refractive index changing portions 157X and 157Y of the core grating portion 155 are formed at the same positions along the optical axis direction.

More specifically, the clad grating portion 154 includes a refractive index changing portion 158X arranged at a grid spacing d ₂ along the optical axis direction and a refractive index changing portion 158Y arranged at a grid spacing d _S. There is. Further, the core grating section 155 includes a refractive index changing section 157X arranged at a grid spacing d ₂ along the optical axis direction and a refractive index changing section 157Y arranged at a grid spacing d _S. For these lattice spacings d ₂ and d _S , _assuming that the effective refractive index of the inner clad layer 52 of the upstream optical filter unit 150 is n _eff52 and the effective refractive index of the core 51 is n _eff51 , the following equation (4) and It is represented by (5).
d ₂ = λ ₂ / (2 × n _eff52 ) ・ ・ ・ (4)
d _S = λ ₃ / (2 × n _eff51 ) ・ ・ ・ (5)

The clad grating portion 154 including the refractive index changing portion 158X arranged at the lattice spacing d ₂ reflects the excitation light P ₂ having a wavelength λ ₂ propagating in the inner clad layer 52. Further, the core grating unit 155 including the refractive index changing unit 157Y arranged at the lattice spacing d _S reflects the signal light L of the wavelength λ ₃ propagating in the core 51. Here, the length in the optical axis direction in which the refractive index changing portion 157Y of the core grating portion 155 exists is sufficiently long so as to reflect the signal light L close to 100%, and the core grating portion 155 is the first. It is designed to function as a high-reflection FBG unit 14 in the embodiment of.

Of the excitation light P ₂ output from the rear excitation light source 22, the excitation light (residual excitation light) P _{2 that} is not absorbed by the core 11 of the amplification optical fiber 10 is located on the upstream side of the amplification optical fiber 10. It propagates through the inner clad layer 52 of the upstream optical filter unit 150. The residual pump light P _2, since it has a wavelength lambda _2, is reflected by the refractive index change portion 158X of the clad grating 154 of the upstream-side filter part 150 described above, the downstream side as a reflected excitation light P ₂ ' Will return to. On the other hand, since the wavelength of the excitation light P ₁ output from the forward excitation light source 21 is λ ₁ and is different from the wavelength λ ₂ , the excitation light P ₁ from the front excitation light source 21 is clad grating of the upstream optical filter unit 150. The part 154 transmits the light as it is without being reflected.

Further, the signal light L generated in the optical resonator 2 propagates through the core 11 of the amplification optical fiber 10 and the core 51 of the upstream optical filter unit 150. Since this signal light L has a wavelength λ ₃ , it is reflected by the refractive index changing unit 157Y of the core grating unit 155 of the upstream side optical filter unit 150 described above.

FIG. 9 is a cross-sectional view schematically showing a configuration when the downstream side optical filter unit 160 is cut along a plane parallel to the optical axis. As shown in FIG. 9, the downstream side optical filter unit 160 of the present embodiment is a modified example of the downstream side optical filter unit 60 of the first embodiment shown in FIG. The inner clad layer 62 of the downstream side optical filter unit 160 has a clad grating portion 164 whose refractive index changes periodically along the optical axis direction, similarly to the downstream side optical filter unit 60. The clad grating portion 164 includes the refractive index changing portions 168X and 168Y having a high refractive index.

Further, in the downstream side optical filter unit 160 of the present embodiment, the core 61 also has a core grating unit 165 whose refractive index changes periodically along the optical axis direction. The core grating section 165 includes refractive index changing sections 167X and 167Y having a high refractive index. The refractive index changing portions 168X and 168Y of the clad grating portion 164 and the refractive index changing portions 167X and 167Y of the core grating portion 165 are formed at the same positions along the optical axis direction.

More specifically, the clad grating portion 164 includes a refractive index changing portion 168X arranged at a grid spacing d ₁ along the optical axis direction and a refractive index changing portion 168Y arranged at a grid spacing d _S. There is. Further, the core grating section 165 includes a refractive index changing section 167X arranged at a grid spacing d ₁ along the optical axis direction and a refractive index changing section 167Y arranged at a grid spacing d _S. These lattice spacing d _1, d _S is the effective refractive index of the inner cladding layer 62 of the downstream-side optical filter 160 and n _Eff62, when the effective refractive index of the core 61 and n _Eff61, the following equation (6) and It is represented by (7).
d ₁ = λ ₁ / (2 × n _eff62 ) ・ ・ ・ (6)
d _S = λ ₃ / (2 × n _eff61 ) ・ ・ ・ (7)

The clad grating portion 164 including the refractive index changing portion 168X arranged at the lattice spacing d ₁ reflects the excitation light P ₁ having a wavelength λ ₁ propagating in the inner clad layer 62. Further, the core grating unit 165 including the refractive index changing unit 167Y arranged at the lattice spacing d _S reflects the signal light L of the wavelength λ ₃ propagating in the core 51. Here, the length of the core grating section 165 in the optical axis direction in which the refractive index changing section 167Y exists is adjusted so as to transmit, for example, about 90% of the signal light L, which is the light L', and the core grating section. 165 functions as the low-reflection FBG unit 16 in the first embodiment.

Of the excitation light P ₁ output from the forward excitation light source 21, the excitation light (residual excitation light) P ₁ not absorbed by the core 11 of the amplification optical fiber 10 is located on the downstream side of the amplification optical fiber 10. It propagates through the inner clad layer 62 of the downstream side optical filter unit 160. The residual pump light P _1, since having a wavelength lambda _1, is reflected by the refractive index change portion 168X of the clad grating 164 of the downstream filter part 160 as described above, the upstream side as the reflected excitation light P ₁ ' Will return to. On the other hand, since the wavelength of the excitation light P ₂ output from the rear excitation light source 22 is λ ₂ and is different from the above wavelength λ ₁ , the excitation light P ₂ from the rear excitation light source 22 is clad grating of the downstream side optical filter unit 160. It is transmitted as it is without being reflected by the part 164.

Further, the signal light L generated in the optical resonator 2 propagates through the core 11 of the amplification optical fiber 10 and the core 61 of the downstream optical filter unit 160. Since this signal light L has a wavelength λ ₃ , most of it is reflected by the refractive index changing part 167Y of the core grating part 165 of the downstream side optical filter part 160, and a part of the light L'(for example, 90). %) Propagates to the downstream side, passes through the delivery fiber 40, and is emitted from the laser emitting portion 41.

In the present embodiment, the refractive index changing portion 157Y of the core grating section 155 of the upstream optical filter section 150 functions as a highly reflective fiber Bragg grating section in the optical resonator 2, and the core grating section 165 of the downstream optical filter section 160 functions. The refractive index changing portion 167Y of the above functions as a low reflection fiber Bragg grating portion in the optical resonator 2. As described above, in the present embodiment, the upstream side optical filter unit 150 can be used as the highly reflective FBG unit 14 constituting the optical resonator 2. Further, the downstream side optical filter unit 160 can be used as the low reflection FBG unit 16 constituting the optical resonator 2. In this case, the upstream side optical filter unit 50 and the high reflection FBG unit 14 in the first embodiment are integrated, and the downstream side optical filter unit 60 and the low reflection FBG unit 16 in the first embodiment are integrated. be able to. Therefore, compared with the case where the upstream side optical filter unit 150 is used separately from the high reflection FBG unit 14 constituting the resonator, or the case where the downstream side optical filter unit 160 is used separately from the low reflection FBG unit 16, fusion connection is performed. By reducing the number of points, the optical loss is reduced, and by reducing the number of parts, the manufacturing cost is reduced.

The upstream side optical filter unit 150 having the clad grating unit 154 and the downstream side optical filter unit 160 having the clad grating unit 164 can be manufactured by the following methods. For example, as shown in FIG. 10A, a core 171 to which Ge, which is a dopant that imparts photosensitivity to SiO ₂ , is added, an inner clad 172 that covers the periphery of the core 171, and an outer clad 173 that covers the periphery of the inner clad 172 are provided. A base material optical fiber (double clad fiber) 170 including the base material is prepared. Ge is added to the inner clad 172 of the base optical fiber 170 in the same manner as the core 171. However, the concentration of Ge added to the inner clad 172 is made lower than the concentration of Ge added to the core 171. Due to this difference in the addition concentration of Ge, the refractive index of the inner clad 172 is lower than that of the core 171. By irradiating such a base optical fiber 170 with light (ultraviolet light) having a periodic intensity distribution along the optical axis direction by using a known method such as a phase mask method or a biluminal interferometry. It is possible to obtain an optical filter portion having a clad grating portion and a core grating portion whose refractive index changes periodically along the optical axis direction. Such an optical filter unit can be used as the upstream side optical filter unit 150 or the downstream side optical filter unit 160 described above.

As another method, as shown in FIG. 10B, a core 181 in which Ge is added to SiO ₂ , an inner clad 182 in which Ge is added at the same concentration as the core 181 and B is also added, and an inner clad. A base optical fiber (double clad fiber) 180 including an outer clad 183 that covers the periphery of the 182 may be used. By irradiating such a base optical fiber 180 with ultraviolet light, it is possible to obtain an optical filter portion having a clad grating portion and a core grating portion whose refractive index changes periodically along the optical axis direction. Such an optical filter unit can be used as the upstream side optical filter unit 150 or the downstream side optical filter unit 160 described above.

FIG. 11 is a schematic block diagram showing the overall configuration of the fiber laser apparatus 201 according to the third embodiment of the present invention. In the present embodiment, as shown in FIG. 11, an upstream side optical filter unit 250 is provided between each of the front excitation light sources 21 and the upstream side light combiner 31, and the rear excitation light sources 22 and the downstream side light are provided. A downstream optical filter unit 260 is provided between the combiner 32 and the combiner 32.

The upstream side optical filter unit 250 allows transmission of the excitation light P ₁ of wavelength λ ₁ output from the front excitation light source 21, but transmits the excitation light P ₂ of wavelength λ ₂ output from the rear excitation light source 22. It is configured to suppress. Further, the upstream side optical filter unit 250 is configured to suppress the transmission of light (signal light) L having a wavelength λ ₃ amplified by the amplification optical fiber 10 of the optical resonator 2. For example, using a specific absorbent, the upstream-side light filter section 250 as the excitation light P ₁ of the pumping light P ₂ and the signal light L is absorbed the wavelength lambda ₁ of the wavelength lambda ₃ of the wavelength lambda ₂ does not absorb Can be configured. Alternatively, it is possible to configure the upstream optical filter portion 250 to separate the light (signal light L having a wavelength lambda ₂ of the pumping light P ₂ and wavelength lambda ₃₎ of a particular wavelength to the outside by using an optical coupler .. Alternatively, a fiber Bragg grating technology described above, the upstream-side filter part to the signal light L of the excitation light P ₂ and wavelength lambda ₃ of the wavelength lambda ₂ is reflected excitation light P ₁ of the wavelength lambda ₁ is transmitted 250 can be configured.

The signal light L amplified by the amplification optical fiber 10 together with the residual excitation light P ₂ that was not absorbed by the core 11 of the amplification optical fiber 10 by the upstream side optical filter unit 250 is the upstream side optical filter unit 250. Propagation to the forward excitation light source 21 beyond the above is suppressed. Therefore, it is possible to reduce the possibility of heat generation and failure of the forward excitation light source 21 due to the residual excitation light P ₂ and the signal light L.

The downstream side optical filter unit 260 allows the transmission of the excitation light P ₂ of the wavelength λ ₂ output from the rear excitation light source 22, but the transmission of the excitation light P ₁ of the wavelength λ ₁ output from the front excitation light source 21. It is configured to suppress. Further, the downstream side optical filter unit 260 is configured to suppress the transmission of light (signal light) L having a wavelength of λ ₃ amplified by the amplification optical fiber 10 of the optical resonator 2. For example, using a specific absorbent, the downstream filter part 260 as the excitation light P ₁ and the signal light L excitation light P ₂ of absorbs the wavelength lambda ₂ wavelength lambda ₃ of the wavelength lambda ₁ does not absorb Can be configured. Alternatively, it is possible to configure the downstream filter part 260 so as to separate the light (signal light L having a wavelength lambda ₁ of the pump light P ₁ and wavelength lambda ₃₎ of a particular wavelength to the outside by using an optical coupler .. Alternatively, a fiber Bragg grating technology described above, the downstream-side filter part to the signal light L having a wavelength lambda ₁ of the pump light P ₁ and wavelength lambda ₃ is reflected excitation light P ₂ having a wavelength lambda ₂ is transmitted 260 can be configured.

The signal light L amplified by the amplification optical fiber 10 together with the residual excitation light P ₁ that was not absorbed by the core 11 of the amplification optical fiber 10 by the downstream side optical filter unit 260 is the downstream side optical filter unit 260. Propagation to the rear excitation light source 22 beyond the above is suppressed. Therefore, it is possible to reduce the possibility of heat generation and failure of the rear excitation light source 22 due to the residual excitation light P ₁ and the signal light L.

It is also possible to apply the above-mentioned optical filter unit to a fiber ring laser device. FIG. 12 is a schematic block diagram showing the overall configuration of the fiber laser device 301 according to the fourth embodiment of the present invention. The fiber laser device 301 of this embodiment is a fiber in which the optical resonator is entirely composed of an optical fiber. It is a ring laser device.

As shown in FIG. 12, the fiber laser apparatus 301 in this embodiment has an optical resonator 302 composed of optical fibers connected in a ring shape. The optical resonator 302 includes an isolator 310 for propagating the signal light L in one direction, an optical switch element 320, and an output optical combiner 330 connected to the laser emitting unit 41 via the delivery fiber 40. There is. The first excitation light source 21 for emitting pumping light P ₁ of the wavelength lambda _1, via the optical combiner 31 is connected to one end of the amplification optical fiber 10, which emits excitation light P ₂ having a wavelength lambda ₂ The second excitation light source 22 is connected to the other end side of the amplification optical fiber 10 via an optical combiner 32.

A first optical filter unit 350 is connected between the optical combiner 31 and the first excitation light source 21, and a second optical filter unit 360 is connected between the optical combiner 32 and the second excitation light source 22. Is connected. The first optical filter unit 350 allows transmission of the excitation light P ₁ of the wavelength λ ₁ output from the first excitation light source 21, but allows the excitation light of the wavelength λ ₂ output from the second excitation light source 22 to pass through. It is configured to suppress the transmission of the signal light L of wavelength λ ₃ amplified by P ₂ and the optical resonator 302. The second optical filter unit 360 allows transmission of the excitation light P ₂ of the wavelength λ ₂ output from the second excitation light source 22, but allows the excitation light of the wavelength λ ₁ output from the first excitation light source 21 to pass through. It is configured to suppress the transmission of the signal light L of wavelength λ ₃ amplified by P ₁ and the optical resonator 302.

The first optical filter unit 350 suppresses the residual excitation light P ₂ not absorbed by the core 11 of the amplification optical fiber 10 from propagating to the excitation light source 21 beyond the first optical filter unit 350. In both cases, the signal light L amplified by the amplification optical fiber 10 is also suppressed from propagating to the first excitation light source 21 beyond the first optical filter unit 350. Therefore, it is possible to reduce the possibility of heat generation and failure of the first excitation light source 21 due to the residual excitation light P ₂ and the signal light L.

Further, the residual excitation light P ₁ not absorbed by the core 11 of the amplification optical fiber 10 is propagated to the second excitation light source 22 beyond the second optical filter unit 360 by the second optical filter unit 360. This is suppressed, and the signal light L amplified by the amplification optical fiber 10 is suppressed from propagating to the second excitation light source 22 beyond the second optical filter unit 360. Therefore, it is possible to reduce the possibility of heat generation and failure of the second excitation light source 22 due to the residual excitation light P ₁ and the signal light L.

In the above-described embodiment, the optical filter unit having two clad layers, the inner clad and the outer clad, has been described, but the number of clad layers in the optical filter unit is not limited to this, and the number of optical filter units is 3. It may have more than one clad layer. Further, in the above-described embodiment, an example in which the inner clad layer of the optical filter portion functions as an excitation optical waveguide clad layer for forming an excitation optical waveguide in which excitation light propagates has been described, but the optical filter portion has three layers. When the above clad layer is provided, any clad layer on which the excitation optical waveguide in which the residual excitation light propagates is formed can be used as the excitation light waveguide clad layer.

Further, in the above-described embodiment, the example in which the optical filter portions are provided on both sides of the amplification optical fiber 10 has been described, but the above-mentioned optical filter portions may be provided only on one side of the amplification optical fiber 10. When the optical filter unit is provided only on one side of the amplification optical fiber 10 in this way, of the forward excitation light source and the rear excitation light source, excitation light having a wavelength having a lower peak of the absorption spectrum for rare earth element ions is generated. Since a large amount of residual excitation light tends to be generated on the side opposite to the side to which the excitation light source is connected, an excitation light source that generates excitation light having a wavelength with a low peak in the absorption spectrum (for example, the rear excitation light source 22 in the example of FIG. 1). It is preferable to provide an optical filter unit on the side opposite to the side to which the light source is connected.

Although the preferred embodiment of the present invention has been described so far, it goes without saying that the present invention is not limited to the above-described embodiment and may be implemented in various different forms within the scope of the technical idea.

1 Fiber laser device 2 Optical resonator 10 Optical fiber for amplification 11 Core 12 Inner clad layer 13 Outer clad layer 14 High reflection FBG part 16 Low reflection FBG part 21 Forward excitation light source (first excitation light source)
22 Rear excitation light source (second excitation light source)
31 Upstream optical combiner (first excitation combiner)
32 Downstream optical combiner (second excitation combiner)
40 Delivery fiber 41 Laser emitting part 50 Upstream side optical filter part (first optical filter part)
51 Core 52 Inner clad layer 53 Outer clad layer 54 Clad grating part 58 Refractive index change part 60 Downstream side optical filter part (second optical filter part)
61 Core 62 Inner clad layer 63 Outer clad layer 64 Clad grating part 68 Refractive index change part 101 Fiber laser device 150 Upstream side optical filter part (first optical filter part)
154 Clad grating section 155 Core grating section 157X, 157Y, 158X, 158Y Refractive index change section 160 Downstream optical filter section (second optical filter section)
164 Clad grating section 165 Core grating section 167X, 167Y, 168X, 168Y Refractive index change section 201 Fiber laser device 250 Upstream optical filter section (first optical filter section)
260 downstream side optical filter section (second optical filter section)
301 Fiber laser device 302 Optical resonator 350 First optical filter unit 360 Second optical filter unit L Signal light P ₁ , P ₂ Excitation light

Claims (15)

An amplification optical fiber including a core to which rare earth element ions are added and a clad layer having an optical waveguide capable of propagating excitation light for exciting the rare earth element ions.
At least one capable of generating a first excitation light having a first wavelength and introducing the first excitation light into the clad layer of the amplification optical fiber from the first end side of the amplification optical fiber. With the first excitation light source,
A second excitation light having a second wavelength different from the first wavelength is generated, and the second end side of the amplification optical fiber is applied to the clad layer of the amplification optical fiber. With at least one second excitation light source capable of introducing excitation light,
A first optical filter unit connected between the at least one first excitation light source and the amplification optical fiber, the second optical filter unit, which allows the transmission of light of the first wavelength. A fiber optic laser apparatus including a first optical filter unit configured to suppress transmission of light of a wavelength. The fiber laser apparatus according to claim 1, wherein the peak of the absorption spectrum for the rare earth element ion at the second wavelength is lower than the peak of the absorption spectrum for the rare earth element ion at the first wavelength. The first optical filter unit is
With the core
With a plurality of clad layers arranged around the core
The core of the first optical filter unit has a core grating unit whose refractive index changes periodically along the optical axis direction so as to reflect light having a wavelength of signal light.
The fiber laser apparatus according to claim 1 or 2. The plurality of clad layers of the first optical filter unit include at least an excitation light propagation clad layer that forms a first excitation optical waveguide through which the first excitation light propagates.
The excitation light propagation clad layer of the first optical filter unit has a clad grating portion whose refractive index periodically changes along the optical axis direction so as to reflect at least a part of the second excitation light. ,
The fiber laser apparatus according to claim 3. The first optical filter unit is
With the core
With a plurality of clad layers arranged around the core
The plurality of clad layers of the first optical filter unit include at least an excitation light propagation clad layer that forms a first excitation optical waveguide through which the first excitation light propagates.
The excitation light propagation clad layer of the first optical filter unit has a clad grating portion whose refractive index periodically changes along the optical axis direction so as to reflect at least a part of the second excitation light. ,
The fiber laser apparatus according to claim 1 or 2. The at least one first excitation light source includes a plurality of first excitation light sources.
The fiber laser device further includes a first optical combiner that combines the first excitation lights from the plurality of first excitation light sources and introduces them into the amplification optical fiber.
The first optical filter unit is provided between the first optical combiner and the amplification optical fiber.
The fiber laser apparatus according to any one of claims 1 to 5. The at least one first excitation light source includes a plurality of first excitation light sources.
The fiber laser device further includes a first optical combiner that combines the first excitation lights from the plurality of first excitation light sources and introduces them into the amplification optical fiber.
The first optical filter unit is connected between at least one of the plurality of first excitation light sources and the first optical combiner.
The fiber laser apparatus according to any one of claims 1 to 5. The fiber laser apparatus according to claim 7, wherein the first optical filter unit is configured to suppress transmission of light having a wavelength of signal light. A second optical filter unit connected between the at least one second excitation light source and the amplification optical fiber, the first of which allows the transmission of light of the second wavelength. The fiber optic laser apparatus according to any one of claims 1 to 8, further comprising a second optical filter unit configured to suppress transmission of light having a wavelength. The second optical filter unit is
With the core
With a plurality of clad layers arranged around the core
The core of the second optical filter unit has a core grating unit whose refractive index changes periodically along the optical axis direction so as to reflect light having a wavelength of signal light.
The fiber laser apparatus according to claim 9. The plurality of clad layers of the second optical filter unit include at least an excitation light propagation clad layer that forms a second excitation optical waveguide through which the second excitation light propagates.
The excitation light propagation clad layer of the second optical filter unit has a clad grating portion whose refractive index periodically changes along the optical axis direction so as to reflect at least a part of the first excitation light. ,
The fiber laser apparatus according to claim 10. The second optical filter unit is
With the core
With a plurality of clad layers arranged around the core
The plurality of clad layers of the second optical filter unit include at least an excitation light propagation clad layer that forms a second excitation optical waveguide through which the second excitation light propagates.
The excitation light propagation clad layer of the second optical filter unit has a clad grating portion whose refractive index periodically changes along the optical axis direction so as to reflect at least a part of the first excitation light. ,
The fiber laser apparatus according to claim 9. The at least one second excitation light source includes a plurality of second excitation light sources.
The fiber laser device further includes a second optical combiner that combines the second excitation lights from the plurality of second excitation light sources and introduces them into the amplification optical fiber.
The second optical filter unit is provided between the second optical combiner and the amplification optical fiber.
The fiber laser apparatus according to any one of claims 9 to 12. The at least one second excitation light source includes a plurality of second excitation light sources.
The fiber laser device further includes a second optical combiner that combines the second excitation lights from the plurality of second excitation light sources and introduces them into the amplification optical fiber.
The second optical filter unit is connected between at least one of the plurality of second excitation light sources and the second optical combiner.
The fiber laser apparatus according to any one of claims 9 to 12. The fiber laser apparatus according to claim 14, wherein the second optical filter unit is configured to suppress transmission of light having a wavelength of signal light.

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